Actually exactly the same energy is returned as is put into the spring - if the spring is made of steel, aluminum, or titanium. Carbon fibre has the distinction as being the one material that can supposedly actually absorb energy from what I understand.
So why worry about frame flex at all? If the frame is moving, so is the rider who is attached. Stand in place and move back and forth gently, for perhaps a few hours - getting tired yet? Even simple movement over a lot of reps can waste energy.
Now, if the frame doesn't flex, why is it a problem? Push on the right pedal standing, the bike flexes left, no push on the left pedal, the bike goes to the right, but the stored energy from the first stroke now augments the pedal stroke - the bike on each stroke is returning energy from the previous stroke making the whole process take place with more of a "snap" if you will. The flex makes the bike feel more lively and as though it has more get-up-and-go. Not convinced? Try standing on a Raleigh hi-ten 3sp frame and go accelerate - nothing there, yet the heavy tubing in theory makes for a very stiff frame.
Now stand and sprint on a frame that is way to flexy for a given rider - the bike doesn't seem to go either - but this time its because your wasting a lot of energy in body movement for the same forward movement as an ideally balanced frame would provide.
The problem is figuring out if a bike doesn't move right for you because the tubes are either too stiff or too flexy. Not easy to figure out. Also, notice that some riders love one frame while others hate it? Comes down to getting the flex just right for the given rider in most cases.
Mike "about to go riding on a bike with carefully chosen tube gauges " Kone in Boulder CO
At 01:57 AM 6/1/02 EDT, GandJFahey@aol.com wrote:
>In a message dated 5/31/02 3:45:49 PM Eastern Daylight Time,
>bikevint@tiac.net writes:
>
>
>spring helps a bike accelerate - but so does
>stiffness perhaps - confused? Yes - it is confusing. Its all about the
>right balance for each rider. Need spring but not too much.
>
>
>
>Doesn't it take at least as much energy to "put the spring into the tube" as
>the amount of spring that is returned? In other words, there's no free
luch.
> No mystic source of energy that automatically bends the tubes into a tensed
>spring position, I think you have to supply the energy even if it springs
>back. ??
>
>The power of placebo is often strong.
>
>Glenn Fahey
>Herndon, VA